1. Unit 12 Viruses & Bacteria

2. Learning Goals
Identify structures and characteristics of Viruses and Bacteria
Explain how viruses and bacteria reproduce
Recognize the importance of viruses and bacteria
Explain how the immune system fights infection

3. Viruses
Infectious particle made of only a strand of DNA or RNA surrounded by a protein coat.
Only contains information on how to reproduce the virus
Protein coat = capsid
Capsid sometimes surrounded by protective lipid envelope

5. Viruses Smaller than bacteria
Non living – cannot reproduce on their own
Need living cells to help them reproduce

6. Viruses Structure and shape play an important role in how they work
Each type can only infect certain hosts
Surface proteins on virus fit to receptor molecules on host cell

7. Virus Shapes - Polyhedral

8. Virus Shapes - Helical

9. Virus Shapes - Enveloped

10. Viruses that infect bacteria
Bacteriophage

11. Virus Life Cycles Lytic cycle
Host cell bursts, releasing new viruses into the host's system, each of which infects another cell

12. STEP
SUMMARY 1.
ATTACHMENT - The lytic virus attaches itself to the host cell. 2.
ENTRY - The virus injects the nucleic acid into the cell. 3.
REPLICATION – virus DNA breaks down host DNA and takes over, instructing cell to make virus parts 4.
ASSEMBLY – Virus parts are put together into new viruses 5.
RELEASE - When viruses are mature, they come out of the cell (destroying it) and start to infect other cells.

14. Virus Life Cycles Lysogenic cycle
virus combines its DNA into the host cell's DNA
Forms a provirus
Virus lays “dormant” as host cell reproduces (remember mitosis S phase)
Trigger can activate the provirus or it can remain a permanent gene

15. STEP
SUMMARY 1.
ATTACHMENT – The virus attaches itself to the host cell. 2.
ENTRY - The virus injects the nucleic acid into the cell. 3.
INTEGRATION – virus DNA becomes part of host cell's DNA 4.
REPLICATION – host cell is replicated with viral DNA

19. Lytic vs. Lysogenic Lytic – causes symptoms very quickly
New viruses are made and spread to other cells right away
Lysogenic – organism may have no symptoms for many years
Once virus is triggered to enter lytic stage symptoms will develop

20. Proviruses Activated when lysogenic virus enters a lytic cycle
Chicken pox → shingles
Cold sores

21. Retroviruses Lysogenic Contain RNA Forces host cell to make viral DNA
Viral DNA is added to host cell's DNA

22. Retroviruses HIV Virus infects white blood cells
AIDS: virus enters lytic cycle → white blood cells are destroyed → body cannot fight off other infections

24. Prions
Infectious particle made only of protein that can cause other proteins to fold incorrectly.
Misfolded proteins will not work
Can incubate for a long time with no symptoms
Once symptoms appear, they worsen quickly and are always fatal
Body has no immune response against a protein

25. Viroids Cause disease in plants
Passed through seeds or pollen
Single stranded RNA without a protein coat
Major economic impact because they can stunt growth in plants

26. Bacteria and Archaea Most abundant organisms on earth
Live in just about every habitat on earth
Prokaryotes

27. Archaea Methanogens Anaerobic Produce methane gas Found in Marshes
Bottom of lakes
Digestive tracts of herbivores

28. Archaea Halophiles Thermoacidophiles Anaerobic
Live in very salty environments
Dead sea, great salt lake
Thermoacidophiles
Live in hot acidic environments
Sulfur springs
Ocean vents

30. Bacteria Heterotrophs Parasitic – feed on living organisms
Saprophytic – feed on dead organisms/waste

31. Bacteria Autotrophs Cyanobacteria – photosynthesizer
Usually blue green
Live in ponds, streams, or other moist areas
Chains of independent cells
Probably earth's 1st oxygen producers
Chemosynthesizers – energy comes from break down of inorganic compounds
Convert atmospheric nitrogen to usable compounds (nitrogen fixation)

33. Bacteria Structure

34. Identifying Bacteria
2 groups based on amount of peptidoglycan in cell wall
Gram negative – thin layer, stain red
Gram positive – thick layer, stain purple

35. Identifying Bacteria Further classified by shape Spherical (cocci)
Rod (basilli)
Spiral (spirilla)
Comma (vibrios)
Corkscrew (spirochates)

36. Reproduction Binary fission asexual Bacteria cell copies its DNA
Both copes of DNA attaches to plasma membrane
Partition forms to create 2 identical new cells
Takes less than 20 minutes under ideal conditions

38. Reproduction Conjugation Sexual
One bacterium transfers part of its chromosome across a pilus
Offspring not genetically identical to parent

39. Bacterial Survival
Endospore – specialized cell with thick, protective wall
Helps cell survive harsh conditions
Can be killed by heating over 100 degrees Celsius

40. Importance of Bacteria
Nitrogen fixation
Digestive tract (probiotics)
Fermenation (cheese, yogurt, pickles)
Bioremediation (breaks down pollutants)